FIG. 1 is a simplified exploded view of a typical prior art mobile telephone at the final assembly stage of its manufacturing. At the heart of the device there is a multilayer printed circuit board or PCB 101 onto which a large number of electronical components (not separately shown) have been soldered. The outer cover of the telephone consists of a front cover 102 and a back cover 103, which are attached to each other by screws or similar attachment means (not separately shown). The PCB may have been previously attached to one of the covers, or the same screws and/or separate alignment pins may serve to fix its position between the covers.
A battery pack 104 is snapped onto the outer side of the back cover where a latch (not separately shown) holds it in position. Onto the lower face of the PCB there has been soldered an appropriate connector (not separately shown) to produce an electrical connection between an attached battery pack and the electronic parts of the mobile telephone through holes in the back cover.
The keypad structure comprises a number of connection points 105 on the PCB surface, an insulating/adhesive film 106 where a punched hole corresponds to each connection point, a metallic domesheet 107 with a dome aligned with each connection point and an elastic keymat 108 where a key bulb corresponds to each key. The adhesive film 106 is two-sided so that it fastens the domesheet 107 onto the surface of the PCB, and the elastic keymat 108 is squeezed between the front cover 102 and the PCB 101 so that the key bulbs become visible on the front side of the telephone through a set of matching holes in the front cover.
The display section of the telephone consists of a LCD (Liquid Crystal Display) unit 109 soldered onto the PCB, a corresponding hole in the front cover 102 and a transparent window 110 which is glued to the front cover. An elastic gasket 111 is squeezed between the outer cover and the LCD unit to absorb mechanical shocks and twisting forces which could easily break the LCD unit which consists mostly of glass.
At the back of the battery compartment there is a SIM holder 112 into which a SIM or Subscriber Identity Module (not separately shown) is to be attached before snapping on the battery pack. A SIM reader 113 has been soldered onto the lower face of the PCB so that the electric connection surfaces of an appropriately input SIM will engage with the corresponding connection springs of the SIM reader.
The prior art construction of FIG. 1 has some drawbacks relating to its mechanical properties as well as to its characteristic requirements to the manufacturing process. The number of mechanically separate units that must be brought together in the final assembly stage is relatively large, which is not advantageous in terms of production logistics and automation. The provision of EMC (ElectroMagnetic Compatibility) shielding for selected components or component groups on the surfaces of the PCB requires separate metallic or metallized covers that should be removably attachable to the PCB. For the gasket of the LCD unit to effectively absorb mechanical shocks and twisting forces its thickness must be at least one millimeter, which makes the display assembly unnecessarily thick for the ultimately miniaturized portable telecommunication devices of today. The SIM reader reserves a relatively large area from the lower surface of the PCB, which adds to the congestion of components on the PCB. Additionally the bending and twisting strength of the mechanical structure is inherently not very high, which in turn dictates that the front and back covers must be made thick to appropriately resist bending and twisting forces.
In an alternative prior art construction some of the above-presented problems have been solved by replacing the simple concave shell-like front and back covers by more complicated shell structures where a number of ridges on their inner surfaces divide the inside of the mobile telephone into compartments. An elastic conductive polymer strip on the protruding edges of the ridges and a matching arrangement of metallized strips on the surface of the PCB provide an electric connection between the PCB and the covers, and a metallized layer on the inside of the covers together with said electrical contact constitutes a set of “EMC vaults” where certain groups of components lie enclosed within a conductive shielding. The ridges also serve as mechanical stiffeners, because they greatly increase the cross-sectional dimensions of the covers. However, they also make the manufacturing and surface treatment processes of the covers much more complicated and seriously limit the possibilities of the manufacturer to use the same covers for different models in a model series where the PCB layout should vary from one model to another. This approach also leaves a significant number of the above-mentioned problems unsolved.